Polaris Posted December 31, 2016 Share Posted December 31, 2016 Hey everyone, after the last time this happened a few months ago and topping the car up with ATF the car has run pretty much like a dream, but would still shudder/stall out if I reversed slowly up a hill. Car drives completely fine otherwise, acceleration feels fine, etc. Today the issue happened again when I was "coasting" without giving it gas into a car wash, and the car stalled out. I don't have any sputtering or stalling at high speeds, this is basically exclusively a problem when I'm in a parking lot coasting around or I coast up to a red light. I also don't have any codes, both a few months ago and now. The car is an automatic Things I have done is look at the A/F ratio on the AP, clean the MAF sensor, check transmission fluid level and appearance (looks decent to me), and check the air filter. Things I have not done yet is just get a ATF change/flush, and maybe see if there are any metal shavings or something in there that might indicate the transmission is screwed? Spark plugs were changed recently, throttle body was cleaned, etc. and I don't think I have a vacuum leak. The major problem is that I can't seem to be able to reproduce this problem consistently. I've taken it to a shop I and a bunch of other car people in my area go to and tried to reproduce it to no avail, and last time I was at Subaru for the airbag recall I told them about it and they checked it out and couldn't find any problems either and couldn't recreate the problem. It's super rare that it happens, but I guess it's "consistently" rare, like I can count on this problem happening at least once out of a few times I drive, but I can't predict when it happens, because sometimes it happens when I'm going up a hill, sometimes just on flat ground, sometimes it doesn't happen at all. Googling as well as searching on LGT here, and looking at suggestions made by other members on here, it seems like the various possibilities include front o2 sensor needs changing, torque converter may be bad, fuel pump is bad, oil control valve problem, vacuum leak, or transmission is about to blow up and I'll be out a few grand. It's super intermittent and if I brake/give it gas the problem starts so I know how to "get rid of it", I just don't want this to be the start of a big problem that costs me a lot in the future/just want to fix it before it gets bad. Right now the two things I am thinking of doing is getting the ATF flushed because it hasn't been changed since the car was new (the car is now at 150k km, or 93k miles ish), as well as change the front o2 sensor as suggested by a couple people last time I asked (I just didn't want to spend unnecessary money haha but I mean if I need to I certainly will) Thank you so much for your help! Link to comment Share on other sites More sharing options...
TheTurboRook Posted January 1, 2017 Share Posted January 1, 2017 So I have been experiencing a similar issue. I bought my car a couple of months ago. It's a 2008 automatic period with only 55,000 miles. If I'm sitting at idle then start to accelerate the car will slightly shutter. Also if I'm driving and have the accelerator down when I let off, the car will slightly shutter as well. It is a physical shutter if that makes sense, meaning I can feel it. It's not a noise shutter or anything like that. I flushed my transmission and change the fluid and that didn't do anything. Some people have suggested that it's possibly the motor mounts going bad so when you're accelerating the car shudders a little as you're adding power to it. I haven't changed my mounts yet so not sure if that'll be a fix Link to comment Share on other sites More sharing options...
Polaris Posted January 1, 2017 Author Share Posted January 1, 2017 Hm, would motor mounts lead to stalling? It's like, shuddering/shaking at low RPMs and speeds, when I'm off the gas, and the car sometimes stalls out as well Link to comment Share on other sites More sharing options...
ehsnils Posted January 1, 2017 Share Posted January 1, 2017 Any correlation to temperature? Does this happen only with a cold engine or is this always happening? I can think of a few simple things to look at; donut gaskets between manifold and cylinder head and the PCV valve. Link to comment Share on other sites More sharing options...
Polaris Posted January 2, 2017 Author Share Posted January 2, 2017 It seems to happen just whenever, whether engine is cold or at normal operating temperatures. The major thing is that it's hard to recreate so even taking it to a mechanic or Subaru itself didn't help :/ I'm just worried like, if the transmission is going to go kaboom. Link to comment Share on other sites More sharing options...
GWagon Posted January 2, 2017 Share Posted January 2, 2017 Can confirm, my 2006 LGT 5eat has done the same thing since 70,000 miles, it only happens every so often. But it feels like right when you apply throttle the rpm's dip so low that the engine stalls out. Weird, and I don't know what causes it! Transmission and spark plugs were replaced at 90,000 miles, I'm currently at 115,000 miles. Link to comment Share on other sites More sharing options...
ehsnils Posted January 2, 2017 Share Posted January 2, 2017 Another item I have experienced on a different brand is the MAP sensor getting gummed up and not being able to measure the pressure in the manifold correctly with the result that the engine was not running well at low rpms. On that car there was also a code for lean mixture though. Link to comment Share on other sites More sharing options...
Polaris Posted January 3, 2017 Author Share Posted January 3, 2017 That makes sense, I could see why that would cause the problems but no codes and monitoring on the AP seems fine but I am extremely far from a "car person". Could a weak battery or alternator cause any of these issues? Also, I did the spark plugs for the first time with a more car-inclined friend of mine this past summer, is it possible we might have messed up the spark plugs somehow? Thanks again! Link to comment Share on other sites More sharing options...
ehsnils Posted January 3, 2017 Share Posted January 3, 2017 Anything is possible, even the spark plugs. Make sure you have the correct plugs, and preferably NGK plugs since they are known to work best. One important thing is to really make sure that the correct plugs are used for the turbo engine and not the NA engine plugs since the thread length on NA plugs is shorter and that means that the gap will be "hidden". At worst the threads may get burnt in the head too. The NGK plug to use is SILFR6A, gapped to 0.8mm (0.032"). Best is to get a completely new set and remove one plug at a time keeping track of which cylinder the old came from and compare the plugs, both with the new plugs to ensure that they look identical and that the old plugs all look similar. Clean the coils too when you do the work, use brake cleaner, not WD-40. WD-40 and similar contains oil that attracts dirt causing misfires too. Link to comment Share on other sites More sharing options...
Polaris Posted January 3, 2017 Author Share Posted January 3, 2017 Yea, I think I got the right ones because I was really paranoid about buying the wrong ones, I got these guys off Rockauto: https://www.rockauto.com/en/moreinfo.php?pk=916838&cc=1430733&jsn=1 The main thing is that it's kind of a general and really vague problem that isn't reproducible on a regular basis, and no codes are being thrown. I don't mind spending some money since I sort of have a "car fund" I save some money into, but I have no idea where to start. It's like should I start with front O2 sensors, get a full ATF flush at a shop, buy a new set of spark plugs (and probably do it at a shop because I don't trust myself anymore), or what if all these are wrong hahaha I'm also getting a bit paranoid if that's the right word and wondering if my battery is going out, or my alternator needs changing, etc. both which are somewhat more expensive than the other things I need to buy. Though I don't think there are any signs those two things are going out, but I'll try to see if my headlights flicker or something like that next time my car tries to stall again. Thanks for your help again! Link to comment Share on other sites More sharing options...
ehsnils Posted January 3, 2017 Share Posted January 3, 2017 Battery/alternator is easy - just check the voltage when the engine is running, it should be in the range of 13.6 to 14.4 volt when idling. Possibly a bit higher, but never above 15 volt. Then check the voltage in the morning before you start the car, if it's below 11.5 (roughly) it may be time to change the battery. Slow cranking combined with indicators varying a lot with the cranking is also an indication of a battery starting to fail. Look at the cheap and simple stuff first, then go to more expensive. And if you haven't checked the PCV valve (tricky to get to but not an expensive item) it's time to do that. Or just replace it with a new one. And clean the ignition coils as well as inspecting them for cracks. It seems like it was the correct spark plugs, so unless they weren't mounted correctly they shouldn't be a problem. Link to comment Share on other sites More sharing options...
altometer Posted January 3, 2017 Share Posted January 3, 2017 I have the same issue. No indicators, no engine codes, no electrical problems. I changed the oil, no vacuum leaks, not bad gas, not a MAF problem, not the fuel pump, not anything sensible. My running theory is it's a combination of the cobb 93 tune, me being catless up and downpipe, and the air tumblers snapping shut. I don't know how many of the engine codes the Cobb tune disables. Link to comment Share on other sites More sharing options...
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